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Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers
w a t e r r e s e a r c h x x x ( 2 0 1 3 ) 1 e1 0
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journal homepage: www.elsevier.com/locate/watres
Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers Tingyi Liu a, Xi Yang a, Zhong-Liang Wang a,b,*, Xiaoxing Yan b a b
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, PR China College of Urban and Environment Science, Tianjin Normal University, Tianjin 300387, PR China
article info
abstract
Article history:
The removal of heavy metals from electroplating wastewater is a matter of paramount
Received 20 December 2012
importance due to their high toxicity causing major environmental pollution problems.
Received in revised form
Nanoscale zero-valent iron (NZVI) became more effective to remove heavy metals from
21 August 2013
electroplating wastewater when enhanced chitosan (CS) beads were introduced as a sup-
Accepted 1 September 2013
port material in permeable reactive barriers (PRBs). The removal rate of Cr (VI) decreased
Available online xxx
with an increase of pH and initial Cr (VI) concentration. However, the removal rates of Cu (II), Cd (II) and Pb (II) increased with an increase of pH while decreased with an increase of
Keywords:
their initial concentrations. The initial concentrations of heavy metals showed an effect on
Nanoscale zero-valent iron (NZVI)
their removal sequence. Scanning electron microscope images showed that CS-NZVI beads
Permeable reactive barriers (PRBs)
enhanced by ethylene glycol diglycidyl ether (EGDE) had a loose and porous surface with a
Ethylene glycol diglycidyl
nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 mm with an
ether (EGDE)
average aperture size of around 58.6 mm. The shell showed a tube structure and electro-
Heavy metals
plating wastewaters may reach NZVI through these tubes. X-ray photoelectron spectro-
Electroplating wastewater
scope (XPS) demonstrated that the reduction of Cr (VI) to Cr (III) was complete in less than 2 h. Cu (II) and Pb (II) were removed via predominant reduction and auxiliary adsorption. However, main adsorption and auxiliary reduction worked for the removal of Cd (II). The removal rate of total Cr, Cu (II), Cd (II) and Pb (II) from actual electroplating wastewater was 89.4%, 98.9%, 94.9% and 99.4%, respectively. The findings revealed that EGDE-CS-NZVIbeads PRBs had the capacity to remediate actual electroplating wastewater and may become an effective and promising technology for in situ remediation of heavy metals. ª 2013 Elsevier Ltd. All rights reserved.
1.
Introduction
Electroplating wastewater contains many kinds of heavy metals, such as Cr, Pb, Cu, Cd, and etc., which are considered
persistent, bioaccumulative and harmful substances (US EPA, 1998; Algarra et al., 2005). Due to the serious threat to human health and ecological systems, these contaminants must be
* Corresponding author. Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, PR China. Tel./fax: þ86 22 23766256. E-mail addresses: [email protected], [email protected], [email protected] (Z.-L. Wang). 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.09.006
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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removed from wastewaters before discharge to the environment (Panayotova et al., 2007). Various remediation technologies have been developed for the removal of the metals from wastewaters (Fu and Wang, 2011). One of the most promising and effective remediation technologies is the use of permeable reactive barriers (PRBs) filled with reactive material(s) for the treatment of contaminated groundwater (Thiruvenkatachari et al., 2008). Owing to low production costs and high efficiency for removal of a wide range of contaminants, zero-valent iron (ZVI) is usually used as a reactive material in engineered PRBs in the form of microscale powders and/or macro scale filings/granules (Choi et al., 2007; Farrell et al., 2000; Scott et al., 2011). Because of its extremely small particle size, large surface area, and high reactivity, nanoscale zero-valent iron (NZVI) has been introduced into wastewaters treatment to remove heavy metals with a much higher efficiency than normal iron powders (Cao and Zhang, 2006; Geng et al., 2009; Kanel et al., 2006). NZVI was applied to remediate wastewaters with a higher removal efficiency in PRBs. However, few studies used NZVI as the reactive media in PRBs. One of the reasons may be that NZVI particles are not easily contained in PRBs due to their extremely small particle size (Joo et al., 2004; Thiruvenkatachari et al., 2008). To overcome these problems, it may be advisable to support NZVI particles on macro-scale and stable composite beads without reducing their reactivity. More recently, NZVI has been supported by chitosan (CS) beads to prepare composite beads with a mean diameter of 3.1 mm (Liu et al., 2010, 2012). Most studies have focused on NZVI synthesis (Zhan et al., 2009), modification (Johnson et al., 2009), and the transport and fate of NZVI in porous media (Phenrat et al., 2009), thus information has been lacking on using CS-NZVI composite beads with a good mechanical strength in PRBs. NZVI has shown high efficiency to remove only one or two kinds of heavy metals in wastewater (Kanel et al., 2006; Liu et al., 2009; Manning et al., 2007; Ponder et al., 2000). However, the interactions between metal ions affected the removal efficiency when several heavy metals co-existed in the wastewaters (McKenzie, 1980; Shama et al., 2010). The goal of the research is to prepare a new and stable system, chitosan/Fe0-nanoparticles beads, as the reactive materials in permeable reactive barriers, for the remediation of electroplating wastewater, containing four heavy metals (Cr, Cu, Cd and Pb). The main objectives were to: (1) synthesize and characterize the new and stable CS-NZVI beads; (2) evaluate the removal efficiency of the co-existing heavy metals by enhanced chitosan/Fe0-nanoparticles beads PRBs under different experimental conditions and (3) investigate the elemental composition and their valence variation during remediation process to reasonably conclude the removal mechanism of co-existing heavy metals in the chitosan/Fe0nanoparticles beads PRBs.
2.
Materials and methods
2.1.
Materials and chemicals
Cellulose powder (20 mm) and chitosan flakes (75% deacetylated) were purchased from Sigma Co. NZVI particles with a
mean diameter of 45.2 nm were purchased from Nanjing Emperor Nano Material Co., Ltd. Ethylene glycol diglycidyl ether (EGDE), K2Cr2O7, CuCl2, CdCl2 and PbCl2 were provided by First Chemical Reagent Manufactory (Tianjin, China). All other chemicals were of analytical grade purity.
2.2.
Preparation of EGDE-CS-NZVI beads
CS-NZVI beads were prepared according to the procedures described in detail elsewhere (Li and Bai, 2005; Liu et al., 2010). Briefly, chitosan flake (2.0 g) was dissolved in 100 mL 1.0% (v/v) acetic acid solution at 60 C and 220 revolutions per min (rpm) for 5 h. Then, a 1.0 g amount of cellulose power was added into the chitosan solution and the mixing was continued for another 5 h at 30 C and 220 rpm. As the chitosan-cellulose solution was cooled down to 20 C, a 1.0 g amount of NZVI was gently added into the solution. Then, the mixture was promptly dropped into a 2 mol/L NaOH solution to form chitosan-cellulose-NZVI beads. The beads were allowed to stand in the deoxygenated NaOH solution for 24 h for hardening and then washed with deionized water. The CS-NZVI beads were stored in deionized water for further use. The beads in stock were put into a beaker with 100 mL deionized water, adjusting pH to 12 by adding 0.1 mol/L NaOH. Then, a 0.8 g of EGDE solution was introduced into the beaker. After continuous agitation at 60 C for 4 h in a thermostatic water bath, the mixture was cooled down to room temperature, and the EGDE-CS-NZVI beads were washed extensively with deionized water to remove any residual cellulose and EGDE. These beads were stored in deionized water for further use. The beads prepared in this way had an average of 3.0 0.04 mm and the water content of the studied material was 89.5% in wet. The whole process was carried out in a nitrogen atmosphere.
2.3.
PRBs experimental set-up and procedure
A laboratory-scale PRBs system was designed using a plexiglass column with 50 cm length and 15 mm internal diameter. The column was filled with the prepared EGDE-CS-NZVI beads as the reactive media and the length of the filler was about 35.6 cm. A 3 cm height of quartz sand (about 0.5 mm diameter) was used to fix the fillers on the top and the bottom, respectively. Electroplating wastewater was continuously pumped into the reactive material column with a downflow mode by peristaltic pump at a flow rate of 60 mL/h. Every 10 min, 1 mL sample was withdrawn using disposable syringes and filtered through a 0.42 mm micro-hole filter. Only one column was constructed due to logistical constraints, meaning that a total of PRBs experimental runs were conducted on the column. Each treatment was replicated three times, with the column completely emptied and repacked between each experiment. After removing the media, the column was soaked in 0.1 mol/L HCl for 24 h and then washed with deionized water 3 times.
2.4. Effects of different experimental conditions on the removal efficiency of heavy metals The pH of the solutions was one of the most important factors in removing heavy metals. The pH was adjusted to 2.88, 4.09,
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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5.12, 6.06, 7.02, 8.06 and 9.20 by adding 0.1 mol/L HCl and NaOH, respectively. In addition, the concentration of heavy metals was also varied at four concentrations. The highest concentration of Cr (VI), Cu (II), Cd (II) and Pb (II) was 100, 100, 75 and 50 mg/L, respectively. These concentrations are extremely high compared with the maximum concentrations allowed in groundwater by the National Quality Standard for Groundwater in China (GB/T 14848-93) (GAQSIQ, 1993), which permit 0.1 mg/L for Cr (VI), 1.5 mg/L for Cu (II), 0.01 mg/L for Cd (II) and 0.1 mg/L for Pb (II). However, the main goal of the test was to evaluate the performance of EGDE-CS-NZVI beads PRBs under extreme contaminated conditions.
2.5. Removal capacity of heavy metals by EGDE-CSNZVI beads PRBs
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The typical wide scan XPS spectra for final products were also investigated.
2.7. Application of EGDE-CS-NZVI beads PRBs to remove heavy metals from electroplating wastewater To explore the feasibility of the removal of heavy metal ions from wastewater, EGDE-CS-NZVI beads PRBs was used to remediate actual electroplating wastewater collected from an electroplate factory’s sewage outfall (Tianjin, China). The wastewater was not treated by any means before being introduced into the EGDE-CS-NZVI-beads PRBs.
3.
Results and discussion
3.1.
Mechanical property of EGDE-CS-NZVI beads
Removal capacity of heavy metals was conducted and the concentration of Cr (VI), Cu (II), Cd (II) and Pb (II) in simulated electroplating wastewater was 20, 20, 15 and 10 mg/L, respectively. The wastewater was continuously pumped into the reactive material column with a downflow mode for 10 h. Samples were withdrawn using disposable syringes at certain time intervals. The Thomas model is used to predict the column breakthrough capacities. The expression of the Thomas model for an adsorption column is as follows (Fu and Viraraghavan, 2003; Vijayaraghavan et al., 2005):
Mechanical strength of EGDE-CS-NZVI beads was determined following a previously reported method (Guo et al., 2004). The deformation ratio is only 2% when the stirring speed reached 800 rpm. In comparison with other studies (Guo et al., 2004; Liu et al., 2012), the conclusion can be reasonably generalized that crumpling ratios are significantly reduced after cross-linking reaction, which indicates that the mechanical strength of EGDE-CS-NZVI beads is enhanced. Thus, it is likely that the new and stable EGDE-CS-NZVI beads will be suitable as the reactive materials in PRBs.
Cout 1 ¼ kTH Cin 1 þ exp Q qeq X Cin Vout
3.2. Removal capacity of heavy metals by EGDE-CSNZVI beads PRBs
(1)
where Cout and Cin represent the concentration of the effluent and influent, respectively. kTH is the Thomas rate constant (mL/min mg), qeq is the maximum solid-phase concentration of the solute (mg/g), Vout is the effluent volume (mL), X is the mass of adsorbent (g), and Q is the flow rate (mL/min). The linearized form of the Thomas model is as equation (2) ¨ ztu¨rk, 2004): (Kavak and O kTH qeq X kCin Vout Cin 1 ¼ ln Cout Q Q
(2)
The kinetic coefficient kTH and the adsorption capacity of the bed qeq can be determined from a plot of ln[(Cin/Cout) 1] against t at a given condition.
2.6. EGDE-CS-NZVI beads characterization and analytical methods The concentration of each heavy metal was measured using inductively coupled air-acetylene flame atomic emission spectrometry (AAF-AES) (WFX-130, BJR Co.). The EGDE-CSNZVI beads were dried by a vacuum freeze drier (BYK FD1A-50, China) at 52 C for 5 h. Morphological analysis of the beads was then performed using a scanning electron microscope (SEM) with energy-dispersive X-ray (EDS) detection (SEM/EDS, FEI Nova NanoSEM 230). The X-ray photoelectron spectroscope (XPS, PHI 5000 Versa Probe) analysis was employed to investigate the elemental composition of the EGDE-CS-NZVI beads before and after heavy metals reduction.
The results of the removal capacity of heavy metals are shown in Fig. 1. Within the reaction time of 6 h, the heavy metals Cr (VI), Cu (II), Cd (II) and Pb (II) can be efficiently removed and all of the removal rates are higher than 96%. Then, the removal rates generally decreased with increasing reaction time, as the redox reaction between heavy metals and NZVI was a chemically controlled and irreversible process (Shi et al., 2011). It also can be seen that there is a steep decrease in the removal rate of Cr (VI) after 6 h (Fig. 1). The pH gradually increased during the reaction process (Table 1), resulting in a decrease in Cr (VI) removal rate (Boddu et al., 2003). Similar phenomena have been observed in other NZVI systems (Liu et al., 2010). However, a significant decrease in the removal rate of Cu (II), Cd (II) and Pb (II) was not observed after 6 h because of the removal rate of Cu (II), Cd (II) and Pb (II) increasing with an increase of pH (Lai and Chen, 2001). As the column saturation/uptake capacity was not observed in this study, a Thomas model is used to predict the column breakthrough capacities (at Ce/C0 ¼ 1), described in detail in other studies (Reynolds and Richards, 1996). According to Thomas model, the removal capacity at the breakthrough point is 44.8, 67.2, 82.6 and 55.8 mg/g for Cr, Cu, Cd and Pb, respectively. The removal capacities obtained in our study are much higher than the results using commercial iron filings or NZVI particles (Genc-Fuhrman et al., 2008; Ponder et al., 2000). It is mainly attributed to the fact that the EGDE-CS-NZVI beads may form the surface films in the PRBs, which in turn causes higher diffusion and adsorption
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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1.0 Cr Cu Cd Pb
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Time (h) Fig. 1 e Removal capacity of heavy metals by EGDE-CSNZVI beads PRBs. Initial concentration: 20 mg/L Cr (VI), 20 mg/L Cu (II), 15 mg/L Cd (II), and 10 mg/L Pb (II); the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements.
than batch experiments (Lai and Chen, 2001). The biofilm has an influence on the transport of stabilized NZVI (Lerner et al., 2012). Due to microbial degradation, ZVI integrated sequencing batch reactor (SBR) resulted in the increased organic removal efficiency compared to the control (Lee et al., 2010). NZVI stimulated methanogenic activity while inhibiting biological dechlorination in a mixed culture containing Dehalococcoides spp (Kirschling et al., 2010; Xiu et al., 2010). The results indicated that EGDE-CS-NZVI beads PRB were effective to remove various heavy metals and a potential promising candidate for applications to in situ environmental remediation.
3.3.
Cr Cu Cd Pb
Effect of pH
A change of pH can influence the reaction rate of iron oxidation and corrosion (Alowitz and Scherer, 2002) and heavy metals can be removed through oxidation or/and complexation with the oxide and hydroxides of iron (Melitas et al., 2001; Shokes and Moller, 1999). The dominant forms of heavy metals in aqueous solution were also affected by pH (Mohan and Pittman, 2006). Thus pH of electroplating wastewater played an important role in removing of heavy metals. The effect of pH on heavy metals removal was conducted and the result is shown in Fig. 2. It is obvious that the removal
Table 1 e The change of the solution pH during the course of adsorption. Initial concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L; NZVI: 10.0 g/L; pH: 2.88; temperature: 20 C. Time (min) pH
0.10
0
10
20
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40
50
60
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3.84
4.92
5.12
5.58
6.18
6.62
Cout/Cin
Cout/Cin
0.6
rates of all heavy metals are higher than 91.8% (Fig. 2), which suggests that EGDE-CS-NZVI beads as a reactive media in PRBs is highly efficient to remove heavy metals from aqueous solutions. It is further noted that with an increase of pH, removal rate of Cr (VI) decreased but the removal rates of Cu (II), Cd (II) and Pb (II) increased. HCrO-4 predominates at pH between 1.0 and 6.0, and CrO4 2 pH above about 6.0 (Mohan and Pittman, 2006). At lower pH the beads were positively charged due to the protonation of amino groups, while Cr (VI) existed mostly as an anion leading to the electrostatic attraction between Cr (VI) and the beads (Boddu et al., 2003). Furthermore, the lower pH could prevent the formation of Fe(III)eCr(III) precipitate. Thus Cr (VI) removal rate decreased with an increase in pH. On the other hand, with increased hydroxyl groups, the number of negatively charged sites was improved, leading to the enhanced attraction force between heavy metals (Cu (II), Cd (II) and Pb (II)) and these beads surface. Therefore, the removal amount of Cu (II), Cd (II) and Pb (II) was increased. The trend is consistent with the reported results by other researchers who investigated the adsorption of heavy metals on the ironcoated sand, CS-NZVI beads and a composite chitosan biosorbent (Boddu et al., 2003; Lai and Chen, 2001; Liu et al., 2010). The change of the solution pH during the reaction was also recorded and the result is shown in Table 1 (Initial concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L; NZVI: 1.0 g/L; pH: 2.88; temperature: 20 C). It can be seen from Table 1 that the solution pH is increased with increasing reaction time. The oxidation of iron and dissolution of Fe(III)eCr(III) precipitate consumed Hþ in the solution, which led to the increase of pH (Alowitz and Scherer, 2002). However, the removal of Cu (II), Cd (II) and Pb (II) also consumed hydroxyl groups. As a result, the final pH value near neutrality was 6.62. This is consistent with the results as observed in Fig. 2.
0.05
0.00 4
6
8
10
pH value Fig. 2 e Effect of pH value on the removal of heavy metals by EGDE-CS-NZVI beads PRBs. Initial concentration: 20 mg/ L Cr (VI), 20 mg/L Cu (II), 15 mg/L Cd (II), and 10 mg/L Pb (II); the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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3.4.
Effect of initial concentrations of heavy metals
Eichhornia crassipes, heavy metals were removed in the order: Pb (II) > Zn (II) > Cd (II) > Cu (II) (Shama et al., 2010). The solution pH is increased as the reaction proceeds, leading to a decrease in Cr (VI) removal (Table 1). However, previous researchers also found that the order was Cu (II) > Pb (II) > Zn (II) > Cd (II) using goethite (McKenzie, 1980).
Heavy metals pollution incidents have occurred repeatedly in recent years (Arao et al., 2010). The concentrations of heavy metals in the incidents were extremely high compared with the maximum concentrations allowed in groundwater. Then, studying on the effect of initial concentrations of heavy metals on the removal efficiency is very important to the applications of EGDE-CS-NZVI beads PRBs. Thus, the effect of initial concentrations of heavy metals was estimated and the result is shown in Fig. 3. It can be observed that the removal rate of Cr (VI), Cu (II), Cd (II), and Pb (II) decreases with an increase of the initial Cr (VI) concentration. With a fixed adsorbent dose, the total available adsorption sites are limited thus leading to a decrease in removal rate of adsorbate corresponding to an increased initial adsorbate concentration (Hiemstra and Van-Riemsdijk, 1999). At the lower concentration (less than 40 mg/L), heavy metals are removed in the order Cd (II) > Cu (II) > Pb (II) > Cr (VI) (Inset of Fig. 3 (a) and (b)). As the concentration increases, the removal order is changed into Pb (II) > Cu (II) > Cd (II) > Cr (VI) (Fig. 3 (c) and (d)). Iron has greater affinity with Pb (II) than Cu (II) in the process of adsorption/oxidation (Lai and Chen, 2001). The similar phenomenon had been reported where heavy metals were adsorbed in the order Pb (II) > Cu (II) > Zn (II) > Cd (II) by hematite (Schwertman and Taylor, 1989). Using
SEM characterization
The morphology of EGDE-CS-NZVI beads is presented in Fig. 4. It can be seen from Fig. 4(a) that the surface of these spherical beads is loose and porous. The particular structure is favorable for mass transfer and energy flow between wastewaters and the EGDE-CS-NZVI beads. There is a nucleus-shell structure inside of these beads in Fig. 4(b). The pore size of the nucleus ranges from 19.2 to 138.6 mm with an average aperture size of around 58.6 mm. According to the previous results (Wan-Ngah and Fatinathan, 2008), the nucleus of the beads is macroporous and the pore sizes in EGDE-CS-NZVI beads are heterogeneous. Other studies pointed out that the uniform reaction between NaOH and acetic acid throughout the beads led to the unique structure inside of the beads (Liu et al., 2010, 2012). The shell shows a tube structure linking the wastewater with NZVI in the beads (Fig. 4(c)) and wastewaters can be introduced into the beads through these tubes. It can be found in Fig. 4(d) that NZVI particles are uniformly distributed in the
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Fig. 3 e Effect of concentrations of heavy metals on the removal of heavy metals by EGDE-CS-NZVI beads PRBs: (a) initial concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L (Inset: expanded chart of (a) at the experimental time from 0.5 to 3 h), (b) initial concentration of Cr (VI): 40 mg/L, Cu (II): 40 mg/L, Cd (II): 30 mg/L, and Pb (II): 20 mg/L (Inset: expanded chart of (b) at the experimental time from 0.5 to 3 h), (c) initial concentration of Cr (VI): 60 mg/L, Cu (II): 60 mg/L, Cd (II): 45 mg/L, and Pb (II): 30 mg/L, and (d) initial concentration of Cr (VI): 100 mg/L, Cu (II): 100 mg/L, Cd (II): 75 mg/L, and Pb (II): 50 mg/L. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements. Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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Fig. 4 e The morphology of EGDE-CS-NZVI beads was analyzed: (a) SEM image of the surface of EGDE-CS-NZVI beads, (b) SEM image of the cross-section of EGDE-CS-NZVI beads, (c) higher magnification of SEM image of the edge of the cross-section, (d) the distribution of NZVI particles in the EGDE-CS-NZVI beads.
EGDE-CS-NZVI beads. It indicates that NZVI supported in EGDE-CS beads can prevent the particles from aggregation. Similar phenomena are also found in other NZVI systems, such as kaolinite-supported NZVI, ECH-CS-NZVI beads (Liu et al., 2012; Uzum et al., 2009).
25000
(b)
Cu
20000
Fe
XPS characterization
The results of XPS characterization were shown in Fig. 5 and Fig. 6. It is clear that new peaks at the binding energy (BE) of 944 eV, 580 eV, 406 eV and 139 eV appeared after heavy metals reduction. The presence of the bands were assigned to the photoelectron peak of Cu, Cr, Cd and Pb, respectively, which indicated the uptake of Cu, Cr, Cd and Pb on the surface of EGDE-CS-NZVI beads. Detailed XPS surveys on the region of Fe2p3/2, Cr2p3/2, Cu2p3/2, Cd3d5/2 and Pb4f7/2 are presented in Fig. 6. Photoelectron peaks at 711.8 and 725.0 eV (Fig. 6 (a)) correspond to the binding energies of 2p3/2 of oxidized iron [Fe (III)]. The peak at 706.5 eV assigned to Fe0 (Chatterjee et al., 2009) was not observed in this study. It indicates that extensive oxidation of iron occurs on the surface of NZVI and little Fe0 remains. The photoelectron peak for Cr2p3/2 centers at 577.2 and 587.6 eV (Fig. 6(b)) which have binding energies and line structures similar to those of Cr (III) (Wan-Ngah et al., 2008). The XPS
15000
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Pb 5000
0 1400
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Fig. 5 e Typical wide scan XPS spectra for the EGDE-CSNZVI beads before and after heavy metals reduction: (a) before heavy metals reduction and (b) after heavy metals reduction. Initial concentration: 60 mg/L Cr (VI), 60 mg/L Cu (II), 45 mg/L Cd (II), and 30 mg/L Pb (II); the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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130
126
Binding Energy (eV) Fig. 6 e High-resolution XPS survey of (a) Fe2p3/2, (b) Cr2p3/2, (c) Cu2p3/2, (d) Cd3d5/2 and (e) Pb4f7/2 of EGDE-CS-NZVI-beads PRBs after reacting with electroplating wastewater for 2 h. Initial concentration of Cr (VI): 100 mg/L, Cu (II): 100 mg/L, Cd (II): 75 mg/L, and Pb (II): 50 mg/L; the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C.
results implied that the reduction of Cr (VI) to Cr (III) was complete in less than 2 h. The new peaks at a BE of 932.4 eV and 952.2 eV can be attributed to the spin-orbit doublet of the Cu2p core level transition (Mekki et al., 1997), which are assigned to Cu (0) and Cu (II) (Fig. 6 (c)), respectively (Li and Bai, 2005). The main peak was known as characteristics of Cu (0) (Fig. 6 (c)). Hence, it was reasonably proposed that Cu (II) was removed predominantly by reduction and the formation of Fe(III)eCu(II) coprecipitated in this study. According to the previous study, at pH > 6, Cu (II) species presenting in the solution were mainly Cu(OH)þ and Cu(OH)2 (Nuhoglu and Oguz, 2003). At pH < 5.7, Cu (II) removal by NZVI conformed to a chemically reductive model, whilst at higher pH (>5.7) removal mechanism of Cu (II) was neither by a reductive or adsorptive model (Scott et al., 2011). Lai and Chen (2001) reported that Cu was
chemisorbed onto iron-coated sand. However, it is also reported that the Cu adsorption on the iron-containing adsorbents was attributed to the formation of strong bonds between Cu (II) and the iron (hydr)oxides (Qian et al., 2009). Similarly, the Cd3d5/2 survey (Fig. 6(d)) presents a photoelectron peak centering at 404.8 and 411.6 eV, which come from Cd (II) and Cd (0), respectively (Li and Zhang, 2007). It is also observed that the peak at 404.8 eV is stronger than that at 411.6 eV, which means that Cd (II) are mainly adsorbed on the EGDE-CS-NZVI beads surface and a small portion of Cd (II) is reduced to Cd (0). Fe(III)eCr(III) hydroxide can be used as an efficient adsorbent material for Cd(II) removal from wastewaters (Namasivayam and Ranganathan, 1995). In fact, the presence of both cationic and anionic species, such as CrO4 2 , CuClþ, CdClþ and PbðNO3 Þþ , caused Cd (II) removal via precipitation of their minerals/salts (Genc-Fuhrman et al., 2008).
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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3.7. Application of EGDE-CS-NZVI beads PRBs for heavy metals removal from actual electroplating wastewater Before the remediation of actual electroplating wastewater, the pH, dissolved oxygen (DO) and chemical oxygen demands (COD) were 4.56, 4.37 mg/L and 1500 mg/L, respectively. The concentrations of total Cr, Cu (II), Cd (II) and Pb (II) in actual electroplating wastewater were 62.6, 55.8, 32.4 and 22.8 mg/L, respectively (Table 2). After treatment by EGDE-CS-NZVIbeads PRBs for 4 h, the pH, DO and COD was 7.56, 1.37 mg/L and 32.4 mg/L, respectively. The pH of actual electroplating wastewater increased, which is consistent with the result of Table 1. The obviously reduction of COD means that the degradable organic matter can be also removed by EGDE-CSNZVI-beads PRBs, which was confirmed by other researchers using NZVI (Giasuddin et al., 2007; Zhang et al., 2011). The removal rate of total Cr, Cu (II), Cd (II) and Pb (II) is 89.4%, 98.9%, 94.9% and 99.4%, respectively (Fig. 7), which is consistent with the results shown in Fig. 3. The result revealed that EGDE-CS-NZVI-beads PRBs had the capacity to remediate actual electroplating wastewater and could become an effective and promising technology for remediation of heavy metals. However, microbial degradation may play an important role in the in situ remediation of heavy metals. Some researchers reported that a chlorophenol-degrading microorganism entrapped in carrageenan-chitosan gels showed a higher bioactivity than free microorganism (Wang and Qian, 1999). Chitosan hydrogel beads could serve as a carrier to deliver macromolecules to the colon (Zhang et al., 2002). In situ remediation combining ZVI and biodegradation has been proposed for the treatment of mixed organic plumes (e.g., chlorinated solvents and petroleum hydrocarbons) (Ma and Zhang, 2008). More attention should be paid to the effect of
Table 2 e The concentration of each heavy metal in actual electroplating wastewater. Wastewater Concentration (mg/L)
Total Cr
Cu(II)
Cd(II)
Pb(II)
62.6
55.8
32.4
22.8
0.12 0.1 0.08
Cout/Cin
In the study, both sorption and reduction are in effect for the removal of Cd (II). Shokes and Moller (1999) proposed that cadmium was rapidly reduced and plated onto the iron surface, which is consist with the result reported by other researchers (Wilkin and McNeil, 2003). However, some researchers reported that Cd (II) was adsorbed on NZVI surface by electrostatic interaction and specific surface bonding (Li and Zhang, 2007). As shown in Fig. 6(e), the Pb4f7/2 has two peaks at 136.0 eV and 138.4 eV, which can be contributed to Pb (0) and Pb (II) (Ponder et al., 2000), respectively. That is, both metillic Pb (0) and Pb (II) are present on the surface of EGDE-CS-NZVI beads. The main peak is known as characteristic of Pb (0). Hence, it is reasonably proposed that both adsorption and predominant reduction are in effect for the removal of Pb (II), conforming the observation of previous studies (Lai and Chen, 2001; Ponder et al., 2000).
0.06 0.04 0.02 0 Cr
Cu
Cd
Pb
Fig. 7 e Application of EGDE-CS-NZVI beads PRBs to remove heavy metals from actual electroplating wastewater. The concentration of NZVI in CS-NZVI: 10.0 g/ L; pH: 4.56; temperature: 20 C. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements.
microbial degradation on the removal of heavy metals by EGDE-CS-NZVI beads in future study.
4.
Conclusions
In this study, NZVI particles is more effective to remove heavy metals from electroplating wastewater when enhanced chitosan beads were introduced as a support material in PRBs. Based on the results, the major finding are summarized as follows: 1) Due to enhanced mechanical strength, the new and stable EGDE-CS-NZVI beads are suitable as the reactive materials in PRBs. 2) With an increase of pH, removal rate of Cr (VI) decreased but the removal rates of Cu (II), Cd (II) and Pb (II) increased. The solution pH increased as the reaction proceeded. 3) The removal rate of Cr (VI), Cu (II), Cd (II), and Pb (II) decreased with an increase of the initial Cr (VI) concentration. At low concentrations (less than 40 mg/L), heavy metals were removed in the order: Cd (II) > Cu (II) > Pb (II) > Cr (VI). As the concentration increased, the removal order was changed into Pb (II) > Cu (II) > Cd (II) > Cr (VI). 4) SEM images showed that with a loose and porous surface, EGDE-CS-NZVI beads showed a nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 mm with an average aperture size of around 58.6 mm. The shell showed a tube structure linking the outside environment with NZVI particles and wastewater could be introduced into the beads through these tubes. 5) The XPS results suggested that extensive oxidation of iron happened on the surface of NZVI and little Fe0 was left. The reduction of Cr (VI) to Cr (III) was complete in less than 2 h. Cu (II) and Pb (II) were removed by predominant reduction and the formation of Fe(III)-heavy metals co-precipitate. However, Cd (II) was mainly adsorbed on the EGDE-CS-
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
w a t e r r e s e a r c h x x x ( 2 0 1 3 ) 1 e1 0
NZVI beads surface and a small portion of Cd (II) was reduced to Cd (0). The result revealed that EGDE-CS-NZVI-beads PRBs had the capacity to remediate actual electroplating wastewater and could become an effective and promising technology for in situ remediation of heavy metals.
Acknowledgments The authors thank Zhigang Zhang, Qian Wang and Fei He for their support with analyses. This work was financially supported by National Science & Technology Pillar Program (2012BAC07B02), National Natural Science Foundation of China (21307090), the University Science & Technology Development Project of Tianjin (20110528), Program for New Century Excellent Talents in University (NCET-10-0954), the Natural Science Foundation of Tianjin (10SYSYJC27400), Foundation of Tianjin Normal University (5RL109, 52XQ1104) and Opening Fund of Tianjin Key Laboratory of Water Resources and Environment (YF11700102).
references
Algarra, M., Jimenez, M.V., Rodriguez-Castellon, E., JimenezLopez, A., Jimenez-Jimenez, J., 2005. Heavy metals removal from electroplating wastewater by aminopropyl-Si MCM-41. Chemosphere 59 (6), 779e786. Alowitz, M.J., Scherer, M.M., 2002. Kinetics of nitrate, nitrite, and Cr (VI) reduction by iron metal. Environ. Sci. Technol. 36 (3), 299e306. Arao, T., Ishikawa, S., Murakami, M., Abe, K., Maejima, Y., Makino, T., 2010. Heavy metal contamination of agricultural soil and countermeasures in Japan. Paddy Water Environ. 8, 247e257. Boddu, V.M., Abburi, K., Talbott, J.L., Smith, E.D., 2003. Removal of hexavalent chromium from wastewater using a new composite chitosan biosorbent. Environ. Sci. Technol. 37 (19), 4449e4456. Cao, J.S., Zhang, W.X., 2006. Stabilization of chromium ore processing residue (COPR) with nanoscale iron particles. J. Hazard. Mater. 132 (2e3), 213e219. Chatterjee, S., Lee, D.S., Lee, M.W., Woo, S.H., 2009. Nitrate removal from aqueous solutions by cross-linked chitosan beads conditioned with sodium bisulfate. J. Hazard. Mater. 166 (1), 508e513. Choi, J.H., Kim, Y.H., Choi, S.J., 2007. Reductive dechlorination and biodegradation of 2,4,6-trichlorophenol using sequential permeable reactive barriers: laboratory studies. Chemosphere 67 (8), 1551e1557. EPA (US Environmental Protection Agency), 1998. Office of Solid Waste Draft PBT Chemical List. EPA/530/D-98/001A. Office of Solid Waste and Emergency Response, Technology Innovation Office, Washington, DC. Farrell, J., Kason, M., Melitas, N., Li, T., 2000. Investigation of the long term performance of zero-valent iron for reductive dechlorination of trichloroethylene. Environ. Sci. Technol. 34 (3), 514e521. Fu, F., Wang, Q., 2011. Removal of heavy metal ions from wastewaters: a review. J. Environ. Manage. 92 (3), 407e418. Fu, Y., Viraraghavan, T., 2003. Column studies for biosorption of dyes from aqueous solutions on immobilised Aspergillus niger fungal biomass. Water SA 29 (4), 465e472.
9
General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (GAQSIQ), 1993. National Quality Standard for Groundwater in China (GB/ T14848-93), pp. 2e3. Genc-Fuhrman, H., Wu, P., Zhou, Y.S., Ledin, A., 2008. Removal of As, Cd, Cr, Cu, Ni and Zn from polluted water using an iron based sorbent. Desalination 226, 357e370. Geng, B., Jin, Z.H., Li, T.L., Qi, X.H., 2009. Kinetics of hexavalent chromium removal from water by chitosan-Fe0 nanoparticles. Chemosphere 75 (6), 825e830. Giasuddin, A.B.M., Kanel, S.R., Choi, H., 2007. Adsorption of humic acid onto nanoscale zerovalent iron and its effect on arsenic removal. Environ. Sci. Technol. 41 (6), 2022e2027. Guo, T.Y., Xia, Y.Q., Hao, G.J., Song, M.D., Zhang, B.H., 2004. Adsorptive separation of hemoglobin by molecularly imprinted chitosan beads. Biomaterials 25 (27), 5905e5912. Hiemstra, T., Van-Riemsdijk, W.H., 1999. Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides. J. Colloid. Interface Sci. 210 (1), 182e193. Johnson, R.L., O’Brien, R.J., Nurmi, J.T., Tratnyek, P.G., 2009. Natural organic matter enhanced mobility of nano zero-valent iron. Environ. Sci. Technol. 43 (14), 5455e5460. Joo, S.H., Feitz, A.J., Waite, T.D., 2004. Oxidative degradation of the carbothioate herbicide, molinate, using nanoscale zero-valent iron. Environ. Sci. Technol. 38 (7), 2242e2247. Kanel, S.R., Greneche, J.M., Choi, H., 2006. Arsenic(V) removal from groundwater using nanoscale zero-valent iron as a colloidal reactive barrier material. Environ. Sci. Technol. 40 (6), 2045e2050. ¨ ztu¨rk, N., 2004. Adsorption of boron from aqueous Kavak, D., O solution by sepirolite: II. column studies. II. illuslrararasi. Bor. Sempozyumu 23e25, 495e500. Kirschling, T.L., Gregory, K.B., Minkley, E.G., Lowry, G.V., Tilton, R.D., 2010. Impact of nanoscale zero-valent iron on geochemistry and microbial populations in trichloroethylene contaminated aquifer materials. Environ. Sci. Technol. 44 (9), 3474e3480. Lai, C.H., Chen, C.Y., 2001. Removal of metal ions and humic acid from water by iron-coated filter media. Chemosphere 44 (5), 1177e1184. Lee, J.W., Cha, D.K., Oh, Y.K., Ko, K.B., Jin, S.H., 2010. Wastewater screening method for evaluating applicability of zero-valent iron to industrial wastewater. J. Hazard. Mater. 180 (1e3), 354e360. Lerner, R.N., Lu, Q., Zeng, H., Liu, Y., 2012. The effects of biofilm on the transport of stabilized zerovalent iron nanoparticles in saturated porous media. Water Res. 46 (4), 975e985. Li, N., Bai, R.B., 2005. Copper adsorption on chitosan-cellulose hydrogel beads: behaviors and mechanisms. Sep. Purif. Technol. 42 (3), 237e247. Li, X.Q., Zhang, W.X., 2007. Sequestration of metals cations with zerovalent iron nanoparticles e a study with high resolution X-ray photoelectron spectroscopy (HR-XPS). J. Phys. Chem. C 111 (19), 6939e6946. Liu, Q.Y., Bei, Y.L., Zhou, F., 2009. Removal of lead (II) from aqueous solution with amino-functionalized nanoscale zerovalent iron. Cent. Eur. Chem. 7 (1), 79e82. Liu, T., Zhao, L., Sun, D.S., Tan, X., 2010. Entrapment of nanoscale zero-valent iron in chitosan beads for hexavalent chromium removal from wastewater. J. Hazard. Mater. 184 (1e3), 724e730. Liu, T., Wang, Z.L., Zhao, L., Yang, X., 2012. Enhanced chitosan/ Fe0-nanoparticles beads for hexavalent chromium removal from wastewater. Chem. Eng. J. 189-190, 196e202. Ma, L.M., Zhang, W.X., 2008. Enhanced biological treatment of industrial wastewater with bimetallic zero-valent iron. Environ. Sci. Technol. 42 (15), 5384e5389. Manning, B.A., Kiser, J.R., Kwon, H., Kanel, S.R., 2007. Spectroscopic investigation of Cr (III) and Cr (VI)-treated nanoscale zero-valent iron. Environ. Sci. Technol. 41, 586e592.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
10
w a t e r r e s e a r c h x x x ( 2 0 1 3 ) 1 e1 0
McKenzie, R.M., 1980. The adsorption of lead and other heavy metals on oxides of manganese and iron. J. Soil Res. 18, 61e73. Mekki, A., Holland, D., McConville, C.F., 1997. X-ray photoelectron spectroscopy study of copper sodium silicate glass surfaces. J. Non-Cryst. Solid 215, 271e282. Melitas, N., Chuffe-Moscoso, O., Farrell, J., 2001. Kinetics of soluble chromium removal from contaminated water by zerovalent iron media: corrosion inhibition and passive oxide effects. Environ. Sci. Technol. 35 (19), 3948e3953. Mohan, D., Pittman, C.U., 2006. Activated carbons and low cost adsorbents for remediation of tri- and hexavalent chromium from water. J. Hazard. Mater. 137, 762e811. Namasivayam, C., Panganathan, K., 1995. Removal of Cd (II) from wastewater by adsorption on “waste” Fe(III)/Cr(III) hydroxide. Water Res. 29 (7), 1737e1744. Nuhoglu, Y., Oguz, E., 2003. Removal of copper (II) from aqueous solutions by biosorption on the cone biomass of Thuja orientalis. Process. Biochem. 38 (11), 1627e1631. Panayotova, T., Dimova-Todorova, M., Dobrevsky, I., 2007. Purification and reuse of heavy metals containing wastewaters from electroplating plants. Desalination 206, 135e140. Phenrat, T., Kim, H.J., Fagerlund, F., Illangasekare, T., Tilton, R.D., Lowry, G.V., 2009. Particle size distribution, concentration, and magnetic attraction affect transport of polymer-modified Fe0 nanoparticles in sand columns. Environ. Sci. Technol. 43 (13), 5079e5085. Ponder, S.M., Darab, J.C., Mallouk, T.E., 2000. Remediation of Cr (VI) and Pb (II) aqueous solutions using supported, nanoscale zero-valent iron. Environ. Sci. Technol. 34 (12), 2564e2569. Qian, Q., Mochidzuki, K., Fujii, T., Sakoda, A., 2009. Removal of copper from aqueous solution using iron-containing adsorbents derived from methane fermentation sludge. J. Hazard. Mater. 172 (2e3), 1137e1144. Reynolds, T.M., Richards, P.S., 1996. Unit Operations and Processes in Environmental Engineering. PSW Publishing Co., Boston, p. 364. Schwertman, U., Taylor, R.M., 1989. Iron oxides. In: Dixon, J.B., Weed, S.B. (Eds.), Minerals in Soil Environments, second ed., pp. 379e428 Soil Sci. Soc. Am. J., Medison, Wisconsin, USA. Scott, T.B., Popescu, I.C., Crane, R.A., Noubactep, C., 2011. Nanoscale metallic iron for the treatment of solutions containing multiple inorganic contaminants. J. Hazard. Mater. 186 (1), 280e287. Shama, S.A., Moustafa, M.E., Gad, M.A., 2010. Removal of heavy metals Fe3þ, Cu2þ, Zn2þ, Pb2þ, Cr3þ and Cd2þ from aqueous solutions by using eichhornia crassipes. Portugaliae Electrochim. Acta 28 (2), 125e133.
Shi, L.N., Zhang, X., Chen, Z.L., 2011. Removal of chromium (VI) from wastewater using bentonite-supported nanoscale zerovalent iron. Water Res. 45 (2), 886e892. Shokes, T.E., Moller, G., 1999. Removal of dissolved heavy metals from acid rock drainage using iron metal. Environ. Sci. Technol. 33 (2), 282e287. Thiruvenkatachari, R., Vigneswaran, S., Naidu, R., 2008. Permeable reactive barrier for groundwater remediation. J. Ind. Eng. Chem. 14 (2), 145e156. Uzum, C., Shahwan, T., Erolu, A.E., Hallam, K.R., Scott, T.B., Lieberwirth, I., 2009. Synthesis and characterization of kaolinite-supported zero-valent iron nanoparticles and their application for the removal of aqueous Cu2þ and Co2þ ions. Appl. Clay Sci. 43 (2), 172e181. Vijayaraghavan, K., Jegan, J., Palanivelu, K., Velan, M., 2005. Batch and column removal of copper from aqueous solution using a brown marine alga Turbinaria ornate. Chem. Eng. J. 106 (2), 177e184. Wang, J., Qian, Y., 1999. Microbial degradation of 4-chlorophenol by microorganisms entrapped in carrageenan-chitosan gels. Chemosphere 38 (13), 3109e3117. Wan-Ngah, W.S., Fatinathan, S., 2008. Adsorption of Cu (II) ions in aqueous solution using chitosan beads, chitosan-GLA beads and chitosan-alginate beads. Chem. Eng. J. 143 (1e3), 62e72. Wan-Ngah, W.S., Hanafiah, M.A.K.M., Yong, S.S., 2008. Adsorption of humic acid from aqueous solutions on crosslinked chitosan-epichlorohydrin beads: kinetics and isotherm studies. Colloid Surf. B 65 (1), 18e24. Wilkin, R.T., McNeil, M.S., 2003. Laboratory evaluation of zerovalent iron to treat water impacted by acid mine drainage. Chemosphere 53 (7), 715e725. Xiu, Z.M., Jin, Z.H., Li, T.L., Mahendra, S., Lowry, G.V., Alvarez, P.J.J., 2010. Effects of nanoscale zero-valent iron particles on a mixed culture dechlorinating trichloroethylene. Bioresour. Technol. 101 (4), 1141e1146. Zhan, J., Sunkara, B., Le, L., John, V.T., He, J., McPherson, G.L., Piringer, G., Lu, Y., 2009. Multifunctional colloidal particles for in situ remediation of chlorinated hydrocarbons. Environ. Sci. Technol. 43 (22), 8616e8621. Zhang, H., Alsarra, I.A., Neau, S.H., 2002. An in vitro evaluation of a chitosan-containing multiparticulate system for macromolecule delivery to the colon. Int. J. Pharm. 239, 197e205. Zhang, M., He, F., Zhao, D., Hao, X., 2011. Degradation of soilsorbed trichloroethylene by stabilized zero valent iron nanoparticles: effects of sorption, surfactants, and natural organic matter. Water Res. 45 (7), 2401e2414.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers Tingyi Liu a, Xi Yang a, Zhong-Liang Wang a,b,*, Xiaoxing Yan b a b
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, PR China College of Urban and Environment Science, Tianjin Normal University, Tianjin 300387, PR China
article info
abstract
Article history:
The removal of heavy metals from electroplating wastewater is a matter of paramount
Received 20 December 2012
importance due to their high toxicity causing major environmental pollution problems.
Received in revised form
Nanoscale zero-valent iron (NZVI) became more effective to remove heavy metals from
21 August 2013
electroplating wastewater when enhanced chitosan (CS) beads were introduced as a sup-
Accepted 1 September 2013
port material in permeable reactive barriers (PRBs). The removal rate of Cr (VI) decreased
Available online xxx
with an increase of pH and initial Cr (VI) concentration. However, the removal rates of Cu (II), Cd (II) and Pb (II) increased with an increase of pH while decreased with an increase of
Keywords:
their initial concentrations. The initial concentrations of heavy metals showed an effect on
Nanoscale zero-valent iron (NZVI)
their removal sequence. Scanning electron microscope images showed that CS-NZVI beads
Permeable reactive barriers (PRBs)
enhanced by ethylene glycol diglycidyl ether (EGDE) had a loose and porous surface with a
Ethylene glycol diglycidyl
nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 mm with an
ether (EGDE)
average aperture size of around 58.6 mm. The shell showed a tube structure and electro-
Heavy metals
plating wastewaters may reach NZVI through these tubes. X-ray photoelectron spectro-
Electroplating wastewater
scope (XPS) demonstrated that the reduction of Cr (VI) to Cr (III) was complete in less than 2 h. Cu (II) and Pb (II) were removed via predominant reduction and auxiliary adsorption. However, main adsorption and auxiliary reduction worked for the removal of Cd (II). The removal rate of total Cr, Cu (II), Cd (II) and Pb (II) from actual electroplating wastewater was 89.4%, 98.9%, 94.9% and 99.4%, respectively. The findings revealed that EGDE-CS-NZVIbeads PRBs had the capacity to remediate actual electroplating wastewater and may become an effective and promising technology for in situ remediation of heavy metals. ª 2013 Elsevier Ltd. All rights reserved.
1.
Introduction
Electroplating wastewater contains many kinds of heavy metals, such as Cr, Pb, Cu, Cd, and etc., which are considered
persistent, bioaccumulative and harmful substances (US EPA, 1998; Algarra et al., 2005). Due to the serious threat to human health and ecological systems, these contaminants must be
* Corresponding author. Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, PR China. Tel./fax: þ86 22 23766256. E-mail addresses: [email protected], [email protected], [email protected] (Z.-L. Wang). 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.09.006
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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removed from wastewaters before discharge to the environment (Panayotova et al., 2007). Various remediation technologies have been developed for the removal of the metals from wastewaters (Fu and Wang, 2011). One of the most promising and effective remediation technologies is the use of permeable reactive barriers (PRBs) filled with reactive material(s) for the treatment of contaminated groundwater (Thiruvenkatachari et al., 2008). Owing to low production costs and high efficiency for removal of a wide range of contaminants, zero-valent iron (ZVI) is usually used as a reactive material in engineered PRBs in the form of microscale powders and/or macro scale filings/granules (Choi et al., 2007; Farrell et al., 2000; Scott et al., 2011). Because of its extremely small particle size, large surface area, and high reactivity, nanoscale zero-valent iron (NZVI) has been introduced into wastewaters treatment to remove heavy metals with a much higher efficiency than normal iron powders (Cao and Zhang, 2006; Geng et al., 2009; Kanel et al., 2006). NZVI was applied to remediate wastewaters with a higher removal efficiency in PRBs. However, few studies used NZVI as the reactive media in PRBs. One of the reasons may be that NZVI particles are not easily contained in PRBs due to their extremely small particle size (Joo et al., 2004; Thiruvenkatachari et al., 2008). To overcome these problems, it may be advisable to support NZVI particles on macro-scale and stable composite beads without reducing their reactivity. More recently, NZVI has been supported by chitosan (CS) beads to prepare composite beads with a mean diameter of 3.1 mm (Liu et al., 2010, 2012). Most studies have focused on NZVI synthesis (Zhan et al., 2009), modification (Johnson et al., 2009), and the transport and fate of NZVI in porous media (Phenrat et al., 2009), thus information has been lacking on using CS-NZVI composite beads with a good mechanical strength in PRBs. NZVI has shown high efficiency to remove only one or two kinds of heavy metals in wastewater (Kanel et al., 2006; Liu et al., 2009; Manning et al., 2007; Ponder et al., 2000). However, the interactions between metal ions affected the removal efficiency when several heavy metals co-existed in the wastewaters (McKenzie, 1980; Shama et al., 2010). The goal of the research is to prepare a new and stable system, chitosan/Fe0-nanoparticles beads, as the reactive materials in permeable reactive barriers, for the remediation of electroplating wastewater, containing four heavy metals (Cr, Cu, Cd and Pb). The main objectives were to: (1) synthesize and characterize the new and stable CS-NZVI beads; (2) evaluate the removal efficiency of the co-existing heavy metals by enhanced chitosan/Fe0-nanoparticles beads PRBs under different experimental conditions and (3) investigate the elemental composition and their valence variation during remediation process to reasonably conclude the removal mechanism of co-existing heavy metals in the chitosan/Fe0nanoparticles beads PRBs.
2.
Materials and methods
2.1.
Materials and chemicals
Cellulose powder (20 mm) and chitosan flakes (75% deacetylated) were purchased from Sigma Co. NZVI particles with a
mean diameter of 45.2 nm were purchased from Nanjing Emperor Nano Material Co., Ltd. Ethylene glycol diglycidyl ether (EGDE), K2Cr2O7, CuCl2, CdCl2 and PbCl2 were provided by First Chemical Reagent Manufactory (Tianjin, China). All other chemicals were of analytical grade purity.
2.2.
Preparation of EGDE-CS-NZVI beads
CS-NZVI beads were prepared according to the procedures described in detail elsewhere (Li and Bai, 2005; Liu et al., 2010). Briefly, chitosan flake (2.0 g) was dissolved in 100 mL 1.0% (v/v) acetic acid solution at 60 C and 220 revolutions per min (rpm) for 5 h. Then, a 1.0 g amount of cellulose power was added into the chitosan solution and the mixing was continued for another 5 h at 30 C and 220 rpm. As the chitosan-cellulose solution was cooled down to 20 C, a 1.0 g amount of NZVI was gently added into the solution. Then, the mixture was promptly dropped into a 2 mol/L NaOH solution to form chitosan-cellulose-NZVI beads. The beads were allowed to stand in the deoxygenated NaOH solution for 24 h for hardening and then washed with deionized water. The CS-NZVI beads were stored in deionized water for further use. The beads in stock were put into a beaker with 100 mL deionized water, adjusting pH to 12 by adding 0.1 mol/L NaOH. Then, a 0.8 g of EGDE solution was introduced into the beaker. After continuous agitation at 60 C for 4 h in a thermostatic water bath, the mixture was cooled down to room temperature, and the EGDE-CS-NZVI beads were washed extensively with deionized water to remove any residual cellulose and EGDE. These beads were stored in deionized water for further use. The beads prepared in this way had an average of 3.0 0.04 mm and the water content of the studied material was 89.5% in wet. The whole process was carried out in a nitrogen atmosphere.
2.3.
PRBs experimental set-up and procedure
A laboratory-scale PRBs system was designed using a plexiglass column with 50 cm length and 15 mm internal diameter. The column was filled with the prepared EGDE-CS-NZVI beads as the reactive media and the length of the filler was about 35.6 cm. A 3 cm height of quartz sand (about 0.5 mm diameter) was used to fix the fillers on the top and the bottom, respectively. Electroplating wastewater was continuously pumped into the reactive material column with a downflow mode by peristaltic pump at a flow rate of 60 mL/h. Every 10 min, 1 mL sample was withdrawn using disposable syringes and filtered through a 0.42 mm micro-hole filter. Only one column was constructed due to logistical constraints, meaning that a total of PRBs experimental runs were conducted on the column. Each treatment was replicated three times, with the column completely emptied and repacked between each experiment. After removing the media, the column was soaked in 0.1 mol/L HCl for 24 h and then washed with deionized water 3 times.
2.4. Effects of different experimental conditions on the removal efficiency of heavy metals The pH of the solutions was one of the most important factors in removing heavy metals. The pH was adjusted to 2.88, 4.09,
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5.12, 6.06, 7.02, 8.06 and 9.20 by adding 0.1 mol/L HCl and NaOH, respectively. In addition, the concentration of heavy metals was also varied at four concentrations. The highest concentration of Cr (VI), Cu (II), Cd (II) and Pb (II) was 100, 100, 75 and 50 mg/L, respectively. These concentrations are extremely high compared with the maximum concentrations allowed in groundwater by the National Quality Standard for Groundwater in China (GB/T 14848-93) (GAQSIQ, 1993), which permit 0.1 mg/L for Cr (VI), 1.5 mg/L for Cu (II), 0.01 mg/L for Cd (II) and 0.1 mg/L for Pb (II). However, the main goal of the test was to evaluate the performance of EGDE-CS-NZVI beads PRBs under extreme contaminated conditions.
2.5. Removal capacity of heavy metals by EGDE-CSNZVI beads PRBs
3
The typical wide scan XPS spectra for final products were also investigated.
2.7. Application of EGDE-CS-NZVI beads PRBs to remove heavy metals from electroplating wastewater To explore the feasibility of the removal of heavy metal ions from wastewater, EGDE-CS-NZVI beads PRBs was used to remediate actual electroplating wastewater collected from an electroplate factory’s sewage outfall (Tianjin, China). The wastewater was not treated by any means before being introduced into the EGDE-CS-NZVI-beads PRBs.
3.
Results and discussion
3.1.
Mechanical property of EGDE-CS-NZVI beads
Removal capacity of heavy metals was conducted and the concentration of Cr (VI), Cu (II), Cd (II) and Pb (II) in simulated electroplating wastewater was 20, 20, 15 and 10 mg/L, respectively. The wastewater was continuously pumped into the reactive material column with a downflow mode for 10 h. Samples were withdrawn using disposable syringes at certain time intervals. The Thomas model is used to predict the column breakthrough capacities. The expression of the Thomas model for an adsorption column is as follows (Fu and Viraraghavan, 2003; Vijayaraghavan et al., 2005):
Mechanical strength of EGDE-CS-NZVI beads was determined following a previously reported method (Guo et al., 2004). The deformation ratio is only 2% when the stirring speed reached 800 rpm. In comparison with other studies (Guo et al., 2004; Liu et al., 2012), the conclusion can be reasonably generalized that crumpling ratios are significantly reduced after cross-linking reaction, which indicates that the mechanical strength of EGDE-CS-NZVI beads is enhanced. Thus, it is likely that the new and stable EGDE-CS-NZVI beads will be suitable as the reactive materials in PRBs.
Cout 1 ¼ kTH Cin 1 þ exp Q qeq X Cin Vout
3.2. Removal capacity of heavy metals by EGDE-CSNZVI beads PRBs
(1)
where Cout and Cin represent the concentration of the effluent and influent, respectively. kTH is the Thomas rate constant (mL/min mg), qeq is the maximum solid-phase concentration of the solute (mg/g), Vout is the effluent volume (mL), X is the mass of adsorbent (g), and Q is the flow rate (mL/min). The linearized form of the Thomas model is as equation (2) ¨ ztu¨rk, 2004): (Kavak and O kTH qeq X kCin Vout Cin 1 ¼ ln Cout Q Q
(2)
The kinetic coefficient kTH and the adsorption capacity of the bed qeq can be determined from a plot of ln[(Cin/Cout) 1] against t at a given condition.
2.6. EGDE-CS-NZVI beads characterization and analytical methods The concentration of each heavy metal was measured using inductively coupled air-acetylene flame atomic emission spectrometry (AAF-AES) (WFX-130, BJR Co.). The EGDE-CSNZVI beads were dried by a vacuum freeze drier (BYK FD1A-50, China) at 52 C for 5 h. Morphological analysis of the beads was then performed using a scanning electron microscope (SEM) with energy-dispersive X-ray (EDS) detection (SEM/EDS, FEI Nova NanoSEM 230). The X-ray photoelectron spectroscope (XPS, PHI 5000 Versa Probe) analysis was employed to investigate the elemental composition of the EGDE-CS-NZVI beads before and after heavy metals reduction.
The results of the removal capacity of heavy metals are shown in Fig. 1. Within the reaction time of 6 h, the heavy metals Cr (VI), Cu (II), Cd (II) and Pb (II) can be efficiently removed and all of the removal rates are higher than 96%. Then, the removal rates generally decreased with increasing reaction time, as the redox reaction between heavy metals and NZVI was a chemically controlled and irreversible process (Shi et al., 2011). It also can be seen that there is a steep decrease in the removal rate of Cr (VI) after 6 h (Fig. 1). The pH gradually increased during the reaction process (Table 1), resulting in a decrease in Cr (VI) removal rate (Boddu et al., 2003). Similar phenomena have been observed in other NZVI systems (Liu et al., 2010). However, a significant decrease in the removal rate of Cu (II), Cd (II) and Pb (II) was not observed after 6 h because of the removal rate of Cu (II), Cd (II) and Pb (II) increasing with an increase of pH (Lai and Chen, 2001). As the column saturation/uptake capacity was not observed in this study, a Thomas model is used to predict the column breakthrough capacities (at Ce/C0 ¼ 1), described in detail in other studies (Reynolds and Richards, 1996). According to Thomas model, the removal capacity at the breakthrough point is 44.8, 67.2, 82.6 and 55.8 mg/g for Cr, Cu, Cd and Pb, respectively. The removal capacities obtained in our study are much higher than the results using commercial iron filings or NZVI particles (Genc-Fuhrman et al., 2008; Ponder et al., 2000). It is mainly attributed to the fact that the EGDE-CS-NZVI beads may form the surface films in the PRBs, which in turn causes higher diffusion and adsorption
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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1.0 Cr Cu Cd Pb
0.8
0.4 0.2 0.0 0
2
4
6
8
10
Time (h) Fig. 1 e Removal capacity of heavy metals by EGDE-CSNZVI beads PRBs. Initial concentration: 20 mg/L Cr (VI), 20 mg/L Cu (II), 15 mg/L Cd (II), and 10 mg/L Pb (II); the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements.
than batch experiments (Lai and Chen, 2001). The biofilm has an influence on the transport of stabilized NZVI (Lerner et al., 2012). Due to microbial degradation, ZVI integrated sequencing batch reactor (SBR) resulted in the increased organic removal efficiency compared to the control (Lee et al., 2010). NZVI stimulated methanogenic activity while inhibiting biological dechlorination in a mixed culture containing Dehalococcoides spp (Kirschling et al., 2010; Xiu et al., 2010). The results indicated that EGDE-CS-NZVI beads PRB were effective to remove various heavy metals and a potential promising candidate for applications to in situ environmental remediation.
3.3.
Cr Cu Cd Pb
Effect of pH
A change of pH can influence the reaction rate of iron oxidation and corrosion (Alowitz and Scherer, 2002) and heavy metals can be removed through oxidation or/and complexation with the oxide and hydroxides of iron (Melitas et al., 2001; Shokes and Moller, 1999). The dominant forms of heavy metals in aqueous solution were also affected by pH (Mohan and Pittman, 2006). Thus pH of electroplating wastewater played an important role in removing of heavy metals. The effect of pH on heavy metals removal was conducted and the result is shown in Fig. 2. It is obvious that the removal
Table 1 e The change of the solution pH during the course of adsorption. Initial concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L; NZVI: 10.0 g/L; pH: 2.88; temperature: 20 C. Time (min) pH
0.10
0
10
20
30
40
50
60
2.88
3.84
4.92
5.12
5.58
6.18
6.62
Cout/Cin
Cout/Cin
0.6
rates of all heavy metals are higher than 91.8% (Fig. 2), which suggests that EGDE-CS-NZVI beads as a reactive media in PRBs is highly efficient to remove heavy metals from aqueous solutions. It is further noted that with an increase of pH, removal rate of Cr (VI) decreased but the removal rates of Cu (II), Cd (II) and Pb (II) increased. HCrO-4 predominates at pH between 1.0 and 6.0, and CrO4 2 pH above about 6.0 (Mohan and Pittman, 2006). At lower pH the beads were positively charged due to the protonation of amino groups, while Cr (VI) existed mostly as an anion leading to the electrostatic attraction between Cr (VI) and the beads (Boddu et al., 2003). Furthermore, the lower pH could prevent the formation of Fe(III)eCr(III) precipitate. Thus Cr (VI) removal rate decreased with an increase in pH. On the other hand, with increased hydroxyl groups, the number of negatively charged sites was improved, leading to the enhanced attraction force between heavy metals (Cu (II), Cd (II) and Pb (II)) and these beads surface. Therefore, the removal amount of Cu (II), Cd (II) and Pb (II) was increased. The trend is consistent with the reported results by other researchers who investigated the adsorption of heavy metals on the ironcoated sand, CS-NZVI beads and a composite chitosan biosorbent (Boddu et al., 2003; Lai and Chen, 2001; Liu et al., 2010). The change of the solution pH during the reaction was also recorded and the result is shown in Table 1 (Initial concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L; NZVI: 1.0 g/L; pH: 2.88; temperature: 20 C). It can be seen from Table 1 that the solution pH is increased with increasing reaction time. The oxidation of iron and dissolution of Fe(III)eCr(III) precipitate consumed Hþ in the solution, which led to the increase of pH (Alowitz and Scherer, 2002). However, the removal of Cu (II), Cd (II) and Pb (II) also consumed hydroxyl groups. As a result, the final pH value near neutrality was 6.62. This is consistent with the results as observed in Fig. 2.
0.05
0.00 4
6
8
10
pH value Fig. 2 e Effect of pH value on the removal of heavy metals by EGDE-CS-NZVI beads PRBs. Initial concentration: 20 mg/ L Cr (VI), 20 mg/L Cu (II), 15 mg/L Cd (II), and 10 mg/L Pb (II); the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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3.4.
Effect of initial concentrations of heavy metals
Eichhornia crassipes, heavy metals were removed in the order: Pb (II) > Zn (II) > Cd (II) > Cu (II) (Shama et al., 2010). The solution pH is increased as the reaction proceeds, leading to a decrease in Cr (VI) removal (Table 1). However, previous researchers also found that the order was Cu (II) > Pb (II) > Zn (II) > Cd (II) using goethite (McKenzie, 1980).
Heavy metals pollution incidents have occurred repeatedly in recent years (Arao et al., 2010). The concentrations of heavy metals in the incidents were extremely high compared with the maximum concentrations allowed in groundwater. Then, studying on the effect of initial concentrations of heavy metals on the removal efficiency is very important to the applications of EGDE-CS-NZVI beads PRBs. Thus, the effect of initial concentrations of heavy metals was estimated and the result is shown in Fig. 3. It can be observed that the removal rate of Cr (VI), Cu (II), Cd (II), and Pb (II) decreases with an increase of the initial Cr (VI) concentration. With a fixed adsorbent dose, the total available adsorption sites are limited thus leading to a decrease in removal rate of adsorbate corresponding to an increased initial adsorbate concentration (Hiemstra and Van-Riemsdijk, 1999). At the lower concentration (less than 40 mg/L), heavy metals are removed in the order Cd (II) > Cu (II) > Pb (II) > Cr (VI) (Inset of Fig. 3 (a) and (b)). As the concentration increases, the removal order is changed into Pb (II) > Cu (II) > Cd (II) > Cr (VI) (Fig. 3 (c) and (d)). Iron has greater affinity with Pb (II) than Cu (II) in the process of adsorption/oxidation (Lai and Chen, 2001). The similar phenomenon had been reported where heavy metals were adsorbed in the order Pb (II) > Cu (II) > Zn (II) > Cd (II) by hematite (Schwertman and Taylor, 1989). Using
SEM characterization
The morphology of EGDE-CS-NZVI beads is presented in Fig. 4. It can be seen from Fig. 4(a) that the surface of these spherical beads is loose and porous. The particular structure is favorable for mass transfer and energy flow between wastewaters and the EGDE-CS-NZVI beads. There is a nucleus-shell structure inside of these beads in Fig. 4(b). The pore size of the nucleus ranges from 19.2 to 138.6 mm with an average aperture size of around 58.6 mm. According to the previous results (Wan-Ngah and Fatinathan, 2008), the nucleus of the beads is macroporous and the pore sizes in EGDE-CS-NZVI beads are heterogeneous. Other studies pointed out that the uniform reaction between NaOH and acetic acid throughout the beads led to the unique structure inside of the beads (Liu et al., 2010, 2012). The shell shows a tube structure linking the wastewater with NZVI in the beads (Fig. 4(c)) and wastewaters can be introduced into the beads through these tubes. It can be found in Fig. 4(d) that NZVI particles are uniformly distributed in the
1.0
(b) 1.0
0.8
0.8
0.6
0.6
Cout/Cin
Cout/Cin
(a)
3.5.
0.4
0.2
0.2 0.0
0.4
0.0 0
1
2
3
0
1
(d) 1.0
1.0 0.8
Cr (Cin=60mg/L)
0.6
Cd (Cin=45mg/L) Pb (Cin=30mg/L)
Cd(Cin=75mg/L)
0.6
Pb(Cin=50mg/L)
0.4 0.2
0.2 0.0 0.0
Cu(Cin=100mg/L)
Cu (Cin=60mg/L)
0.4
3
Cr(Cin=100mg/L)
0.8
Cout/Cin
Cout/Cin
(c)
2
Time (h)
Time (h)
0.5
1.0
1.5
Time (h)
2.0
2.5
3.0
0.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (h)
Fig. 3 e Effect of concentrations of heavy metals on the removal of heavy metals by EGDE-CS-NZVI beads PRBs: (a) initial concentration of Cr (VI): 20 mg/L, Cu (II): 20 mg/L, Cd (II): 15 mg/L, and Pb (II): 10 mg/L (Inset: expanded chart of (a) at the experimental time from 0.5 to 3 h), (b) initial concentration of Cr (VI): 40 mg/L, Cu (II): 40 mg/L, Cd (II): 30 mg/L, and Pb (II): 20 mg/L (Inset: expanded chart of (b) at the experimental time from 0.5 to 3 h), (c) initial concentration of Cr (VI): 60 mg/L, Cu (II): 60 mg/L, Cd (II): 45 mg/L, and Pb (II): 30 mg/L, and (d) initial concentration of Cr (VI): 100 mg/L, Cu (II): 100 mg/L, Cd (II): 75 mg/L, and Pb (II): 50 mg/L. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements. Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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Fig. 4 e The morphology of EGDE-CS-NZVI beads was analyzed: (a) SEM image of the surface of EGDE-CS-NZVI beads, (b) SEM image of the cross-section of EGDE-CS-NZVI beads, (c) higher magnification of SEM image of the edge of the cross-section, (d) the distribution of NZVI particles in the EGDE-CS-NZVI beads.
EGDE-CS-NZVI beads. It indicates that NZVI supported in EGDE-CS beads can prevent the particles from aggregation. Similar phenomena are also found in other NZVI systems, such as kaolinite-supported NZVI, ECH-CS-NZVI beads (Liu et al., 2012; Uzum et al., 2009).
25000
(b)
Cu
20000
Fe
XPS characterization
The results of XPS characterization were shown in Fig. 5 and Fig. 6. It is clear that new peaks at the binding energy (BE) of 944 eV, 580 eV, 406 eV and 139 eV appeared after heavy metals reduction. The presence of the bands were assigned to the photoelectron peak of Cu, Cr, Cd and Pb, respectively, which indicated the uptake of Cu, Cr, Cd and Pb on the surface of EGDE-CS-NZVI beads. Detailed XPS surveys on the region of Fe2p3/2, Cr2p3/2, Cu2p3/2, Cd3d5/2 and Pb4f7/2 are presented in Fig. 6. Photoelectron peaks at 711.8 and 725.0 eV (Fig. 6 (a)) correspond to the binding energies of 2p3/2 of oxidized iron [Fe (III)]. The peak at 706.5 eV assigned to Fe0 (Chatterjee et al., 2009) was not observed in this study. It indicates that extensive oxidation of iron occurs on the surface of NZVI and little Fe0 remains. The photoelectron peak for Cr2p3/2 centers at 577.2 and 587.6 eV (Fig. 6(b)) which have binding energies and line structures similar to those of Cr (III) (Wan-Ngah et al., 2008). The XPS
15000
O
(a)
C/S
3.6.
C
Cr 10000
Cd
Pb 5000
0 1400
1200
1000 800 600 400 Binding Energy (eV)
200
0
Fig. 5 e Typical wide scan XPS spectra for the EGDE-CSNZVI beads before and after heavy metals reduction: (a) before heavy metals reduction and (b) after heavy metals reduction. Initial concentration: 60 mg/L Cr (VI), 60 mg/L Cu (II), 45 mg/L Cd (II), and 30 mg/L Pb (II); the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
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2500
(a)Fe2p3/2
2400
Fe(III)
1700
(b) Cr2p3/2
1650
Fe(III)
Cr(III)
1600
2300
C/S
C/S
2600
2200
1550 1500
2100
1450
2000
1400
1900
Cr(III)
1350 727 723 719 715 711 707 703
589
585
Binding Energy (eV)
581
3400
Cu(0)
569
(d) Cd3d5/2
950
3200
900
Cu(II)
C/S
C/S
573
1000
(c) Cu2p3/2 3000
577
Binding Energy (eV)
Cd(II) Cd(0)
850 800
2800
750 2600
700 957 953 949 945 941 937 933 929
419
415
Binding Energy (eV) 590
411
407
403
399
Binding Energy (eV)
(e) Pb4f7/2
570
C/S
550
Pb(0)
530 510
Pb(II)
490 470 450 150
146
142
138
134
130
126
Binding Energy (eV) Fig. 6 e High-resolution XPS survey of (a) Fe2p3/2, (b) Cr2p3/2, (c) Cu2p3/2, (d) Cd3d5/2 and (e) Pb4f7/2 of EGDE-CS-NZVI-beads PRBs after reacting with electroplating wastewater for 2 h. Initial concentration of Cr (VI): 100 mg/L, Cu (II): 100 mg/L, Cd (II): 75 mg/L, and Pb (II): 50 mg/L; the concentration of NZVI in CS-NZVI: 10.0 g/L; pH: 6.4; temperature: 20 C.
results implied that the reduction of Cr (VI) to Cr (III) was complete in less than 2 h. The new peaks at a BE of 932.4 eV and 952.2 eV can be attributed to the spin-orbit doublet of the Cu2p core level transition (Mekki et al., 1997), which are assigned to Cu (0) and Cu (II) (Fig. 6 (c)), respectively (Li and Bai, 2005). The main peak was known as characteristics of Cu (0) (Fig. 6 (c)). Hence, it was reasonably proposed that Cu (II) was removed predominantly by reduction and the formation of Fe(III)eCu(II) coprecipitated in this study. According to the previous study, at pH > 6, Cu (II) species presenting in the solution were mainly Cu(OH)þ and Cu(OH)2 (Nuhoglu and Oguz, 2003). At pH < 5.7, Cu (II) removal by NZVI conformed to a chemically reductive model, whilst at higher pH (>5.7) removal mechanism of Cu (II) was neither by a reductive or adsorptive model (Scott et al., 2011). Lai and Chen (2001) reported that Cu was
chemisorbed onto iron-coated sand. However, it is also reported that the Cu adsorption on the iron-containing adsorbents was attributed to the formation of strong bonds between Cu (II) and the iron (hydr)oxides (Qian et al., 2009). Similarly, the Cd3d5/2 survey (Fig. 6(d)) presents a photoelectron peak centering at 404.8 and 411.6 eV, which come from Cd (II) and Cd (0), respectively (Li and Zhang, 2007). It is also observed that the peak at 404.8 eV is stronger than that at 411.6 eV, which means that Cd (II) are mainly adsorbed on the EGDE-CS-NZVI beads surface and a small portion of Cd (II) is reduced to Cd (0). Fe(III)eCr(III) hydroxide can be used as an efficient adsorbent material for Cd(II) removal from wastewaters (Namasivayam and Ranganathan, 1995). In fact, the presence of both cationic and anionic species, such as CrO4 2 , CuClþ, CdClþ and PbðNO3 Þþ , caused Cd (II) removal via precipitation of their minerals/salts (Genc-Fuhrman et al., 2008).
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3.7. Application of EGDE-CS-NZVI beads PRBs for heavy metals removal from actual electroplating wastewater Before the remediation of actual electroplating wastewater, the pH, dissolved oxygen (DO) and chemical oxygen demands (COD) were 4.56, 4.37 mg/L and 1500 mg/L, respectively. The concentrations of total Cr, Cu (II), Cd (II) and Pb (II) in actual electroplating wastewater were 62.6, 55.8, 32.4 and 22.8 mg/L, respectively (Table 2). After treatment by EGDE-CS-NZVIbeads PRBs for 4 h, the pH, DO and COD was 7.56, 1.37 mg/L and 32.4 mg/L, respectively. The pH of actual electroplating wastewater increased, which is consistent with the result of Table 1. The obviously reduction of COD means that the degradable organic matter can be also removed by EGDE-CSNZVI-beads PRBs, which was confirmed by other researchers using NZVI (Giasuddin et al., 2007; Zhang et al., 2011). The removal rate of total Cr, Cu (II), Cd (II) and Pb (II) is 89.4%, 98.9%, 94.9% and 99.4%, respectively (Fig. 7), which is consistent with the results shown in Fig. 3. The result revealed that EGDE-CS-NZVI-beads PRBs had the capacity to remediate actual electroplating wastewater and could become an effective and promising technology for remediation of heavy metals. However, microbial degradation may play an important role in the in situ remediation of heavy metals. Some researchers reported that a chlorophenol-degrading microorganism entrapped in carrageenan-chitosan gels showed a higher bioactivity than free microorganism (Wang and Qian, 1999). Chitosan hydrogel beads could serve as a carrier to deliver macromolecules to the colon (Zhang et al., 2002). In situ remediation combining ZVI and biodegradation has been proposed for the treatment of mixed organic plumes (e.g., chlorinated solvents and petroleum hydrocarbons) (Ma and Zhang, 2008). More attention should be paid to the effect of
Table 2 e The concentration of each heavy metal in actual electroplating wastewater. Wastewater Concentration (mg/L)
Total Cr
Cu(II)
Cd(II)
Pb(II)
62.6
55.8
32.4
22.8
0.12 0.1 0.08
Cout/Cin
In the study, both sorption and reduction are in effect for the removal of Cd (II). Shokes and Moller (1999) proposed that cadmium was rapidly reduced and plated onto the iron surface, which is consist with the result reported by other researchers (Wilkin and McNeil, 2003). However, some researchers reported that Cd (II) was adsorbed on NZVI surface by electrostatic interaction and specific surface bonding (Li and Zhang, 2007). As shown in Fig. 6(e), the Pb4f7/2 has two peaks at 136.0 eV and 138.4 eV, which can be contributed to Pb (0) and Pb (II) (Ponder et al., 2000), respectively. That is, both metillic Pb (0) and Pb (II) are present on the surface of EGDE-CS-NZVI beads. The main peak is known as characteristic of Pb (0). Hence, it is reasonably proposed that both adsorption and predominant reduction are in effect for the removal of Pb (II), conforming the observation of previous studies (Lai and Chen, 2001; Ponder et al., 2000).
0.06 0.04 0.02 0 Cr
Cu
Cd
Pb
Fig. 7 e Application of EGDE-CS-NZVI beads PRBs to remove heavy metals from actual electroplating wastewater. The concentration of NZVI in CS-NZVI: 10.0 g/ L; pH: 4.56; temperature: 20 C. Cout and Cin represented the concentration of the effluent and influent, respectively. Error bars represent the standard deviation of the measurements.
microbial degradation on the removal of heavy metals by EGDE-CS-NZVI beads in future study.
4.
Conclusions
In this study, NZVI particles is more effective to remove heavy metals from electroplating wastewater when enhanced chitosan beads were introduced as a support material in PRBs. Based on the results, the major finding are summarized as follows: 1) Due to enhanced mechanical strength, the new and stable EGDE-CS-NZVI beads are suitable as the reactive materials in PRBs. 2) With an increase of pH, removal rate of Cr (VI) decreased but the removal rates of Cu (II), Cd (II) and Pb (II) increased. The solution pH increased as the reaction proceeded. 3) The removal rate of Cr (VI), Cu (II), Cd (II), and Pb (II) decreased with an increase of the initial Cr (VI) concentration. At low concentrations (less than 40 mg/L), heavy metals were removed in the order: Cd (II) > Cu (II) > Pb (II) > Cr (VI). As the concentration increased, the removal order was changed into Pb (II) > Cu (II) > Cd (II) > Cr (VI). 4) SEM images showed that with a loose and porous surface, EGDE-CS-NZVI beads showed a nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 mm with an average aperture size of around 58.6 mm. The shell showed a tube structure linking the outside environment with NZVI particles and wastewater could be introduced into the beads through these tubes. 5) The XPS results suggested that extensive oxidation of iron happened on the surface of NZVI and little Fe0 was left. The reduction of Cr (VI) to Cr (III) was complete in less than 2 h. Cu (II) and Pb (II) were removed by predominant reduction and the formation of Fe(III)-heavy metals co-precipitate. However, Cd (II) was mainly adsorbed on the EGDE-CS-
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
w a t e r r e s e a r c h x x x ( 2 0 1 3 ) 1 e1 0
NZVI beads surface and a small portion of Cd (II) was reduced to Cd (0). The result revealed that EGDE-CS-NZVI-beads PRBs had the capacity to remediate actual electroplating wastewater and could become an effective and promising technology for in situ remediation of heavy metals.
Acknowledgments The authors thank Zhigang Zhang, Qian Wang and Fei He for their support with analyses. This work was financially supported by National Science & Technology Pillar Program (2012BAC07B02), National Natural Science Foundation of China (21307090), the University Science & Technology Development Project of Tianjin (20110528), Program for New Century Excellent Talents in University (NCET-10-0954), the Natural Science Foundation of Tianjin (10SYSYJC27400), Foundation of Tianjin Normal University (5RL109, 52XQ1104) and Opening Fund of Tianjin Key Laboratory of Water Resources and Environment (YF11700102).
references
Algarra, M., Jimenez, M.V., Rodriguez-Castellon, E., JimenezLopez, A., Jimenez-Jimenez, J., 2005. Heavy metals removal from electroplating wastewater by aminopropyl-Si MCM-41. Chemosphere 59 (6), 779e786. Alowitz, M.J., Scherer, M.M., 2002. Kinetics of nitrate, nitrite, and Cr (VI) reduction by iron metal. Environ. Sci. Technol. 36 (3), 299e306. Arao, T., Ishikawa, S., Murakami, M., Abe, K., Maejima, Y., Makino, T., 2010. Heavy metal contamination of agricultural soil and countermeasures in Japan. Paddy Water Environ. 8, 247e257. Boddu, V.M., Abburi, K., Talbott, J.L., Smith, E.D., 2003. Removal of hexavalent chromium from wastewater using a new composite chitosan biosorbent. Environ. Sci. Technol. 37 (19), 4449e4456. Cao, J.S., Zhang, W.X., 2006. Stabilization of chromium ore processing residue (COPR) with nanoscale iron particles. J. Hazard. Mater. 132 (2e3), 213e219. Chatterjee, S., Lee, D.S., Lee, M.W., Woo, S.H., 2009. Nitrate removal from aqueous solutions by cross-linked chitosan beads conditioned with sodium bisulfate. J. Hazard. Mater. 166 (1), 508e513. Choi, J.H., Kim, Y.H., Choi, S.J., 2007. Reductive dechlorination and biodegradation of 2,4,6-trichlorophenol using sequential permeable reactive barriers: laboratory studies. Chemosphere 67 (8), 1551e1557. EPA (US Environmental Protection Agency), 1998. Office of Solid Waste Draft PBT Chemical List. EPA/530/D-98/001A. Office of Solid Waste and Emergency Response, Technology Innovation Office, Washington, DC. Farrell, J., Kason, M., Melitas, N., Li, T., 2000. Investigation of the long term performance of zero-valent iron for reductive dechlorination of trichloroethylene. Environ. Sci. Technol. 34 (3), 514e521. Fu, F., Wang, Q., 2011. Removal of heavy metal ions from wastewaters: a review. J. Environ. Manage. 92 (3), 407e418. Fu, Y., Viraraghavan, T., 2003. Column studies for biosorption of dyes from aqueous solutions on immobilised Aspergillus niger fungal biomass. Water SA 29 (4), 465e472.
9
General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (GAQSIQ), 1993. National Quality Standard for Groundwater in China (GB/ T14848-93), pp. 2e3. Genc-Fuhrman, H., Wu, P., Zhou, Y.S., Ledin, A., 2008. Removal of As, Cd, Cr, Cu, Ni and Zn from polluted water using an iron based sorbent. Desalination 226, 357e370. Geng, B., Jin, Z.H., Li, T.L., Qi, X.H., 2009. Kinetics of hexavalent chromium removal from water by chitosan-Fe0 nanoparticles. Chemosphere 75 (6), 825e830. Giasuddin, A.B.M., Kanel, S.R., Choi, H., 2007. Adsorption of humic acid onto nanoscale zerovalent iron and its effect on arsenic removal. Environ. Sci. Technol. 41 (6), 2022e2027. Guo, T.Y., Xia, Y.Q., Hao, G.J., Song, M.D., Zhang, B.H., 2004. Adsorptive separation of hemoglobin by molecularly imprinted chitosan beads. Biomaterials 25 (27), 5905e5912. Hiemstra, T., Van-Riemsdijk, W.H., 1999. Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides. J. Colloid. Interface Sci. 210 (1), 182e193. Johnson, R.L., O’Brien, R.J., Nurmi, J.T., Tratnyek, P.G., 2009. Natural organic matter enhanced mobility of nano zero-valent iron. Environ. Sci. Technol. 43 (14), 5455e5460. Joo, S.H., Feitz, A.J., Waite, T.D., 2004. Oxidative degradation of the carbothioate herbicide, molinate, using nanoscale zero-valent iron. Environ. Sci. Technol. 38 (7), 2242e2247. Kanel, S.R., Greneche, J.M., Choi, H., 2006. Arsenic(V) removal from groundwater using nanoscale zero-valent iron as a colloidal reactive barrier material. Environ. Sci. Technol. 40 (6), 2045e2050. ¨ ztu¨rk, N., 2004. Adsorption of boron from aqueous Kavak, D., O solution by sepirolite: II. column studies. II. illuslrararasi. Bor. Sempozyumu 23e25, 495e500. Kirschling, T.L., Gregory, K.B., Minkley, E.G., Lowry, G.V., Tilton, R.D., 2010. Impact of nanoscale zero-valent iron on geochemistry and microbial populations in trichloroethylene contaminated aquifer materials. Environ. Sci. Technol. 44 (9), 3474e3480. Lai, C.H., Chen, C.Y., 2001. Removal of metal ions and humic acid from water by iron-coated filter media. Chemosphere 44 (5), 1177e1184. Lee, J.W., Cha, D.K., Oh, Y.K., Ko, K.B., Jin, S.H., 2010. Wastewater screening method for evaluating applicability of zero-valent iron to industrial wastewater. J. Hazard. Mater. 180 (1e3), 354e360. Lerner, R.N., Lu, Q., Zeng, H., Liu, Y., 2012. The effects of biofilm on the transport of stabilized zerovalent iron nanoparticles in saturated porous media. Water Res. 46 (4), 975e985. Li, N., Bai, R.B., 2005. Copper adsorption on chitosan-cellulose hydrogel beads: behaviors and mechanisms. Sep. Purif. Technol. 42 (3), 237e247. Li, X.Q., Zhang, W.X., 2007. Sequestration of metals cations with zerovalent iron nanoparticles e a study with high resolution X-ray photoelectron spectroscopy (HR-XPS). J. Phys. Chem. C 111 (19), 6939e6946. Liu, Q.Y., Bei, Y.L., Zhou, F., 2009. Removal of lead (II) from aqueous solution with amino-functionalized nanoscale zerovalent iron. Cent. Eur. Chem. 7 (1), 79e82. Liu, T., Zhao, L., Sun, D.S., Tan, X., 2010. Entrapment of nanoscale zero-valent iron in chitosan beads for hexavalent chromium removal from wastewater. J. Hazard. Mater. 184 (1e3), 724e730. Liu, T., Wang, Z.L., Zhao, L., Yang, X., 2012. Enhanced chitosan/ Fe0-nanoparticles beads for hexavalent chromium removal from wastewater. Chem. Eng. J. 189-190, 196e202. Ma, L.M., Zhang, W.X., 2008. Enhanced biological treatment of industrial wastewater with bimetallic zero-valent iron. Environ. Sci. Technol. 42 (15), 5384e5389. Manning, B.A., Kiser, J.R., Kwon, H., Kanel, S.R., 2007. Spectroscopic investigation of Cr (III) and Cr (VI)-treated nanoscale zero-valent iron. Environ. Sci. Technol. 41, 586e592.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006
10
w a t e r r e s e a r c h x x x ( 2 0 1 3 ) 1 e1 0
McKenzie, R.M., 1980. The adsorption of lead and other heavy metals on oxides of manganese and iron. J. Soil Res. 18, 61e73. Mekki, A., Holland, D., McConville, C.F., 1997. X-ray photoelectron spectroscopy study of copper sodium silicate glass surfaces. J. Non-Cryst. Solid 215, 271e282. Melitas, N., Chuffe-Moscoso, O., Farrell, J., 2001. Kinetics of soluble chromium removal from contaminated water by zerovalent iron media: corrosion inhibition and passive oxide effects. Environ. Sci. Technol. 35 (19), 3948e3953. Mohan, D., Pittman, C.U., 2006. Activated carbons and low cost adsorbents for remediation of tri- and hexavalent chromium from water. J. Hazard. Mater. 137, 762e811. Namasivayam, C., Panganathan, K., 1995. Removal of Cd (II) from wastewater by adsorption on “waste” Fe(III)/Cr(III) hydroxide. Water Res. 29 (7), 1737e1744. Nuhoglu, Y., Oguz, E., 2003. Removal of copper (II) from aqueous solutions by biosorption on the cone biomass of Thuja orientalis. Process. Biochem. 38 (11), 1627e1631. Panayotova, T., Dimova-Todorova, M., Dobrevsky, I., 2007. Purification and reuse of heavy metals containing wastewaters from electroplating plants. Desalination 206, 135e140. Phenrat, T., Kim, H.J., Fagerlund, F., Illangasekare, T., Tilton, R.D., Lowry, G.V., 2009. Particle size distribution, concentration, and magnetic attraction affect transport of polymer-modified Fe0 nanoparticles in sand columns. Environ. Sci. Technol. 43 (13), 5079e5085. Ponder, S.M., Darab, J.C., Mallouk, T.E., 2000. Remediation of Cr (VI) and Pb (II) aqueous solutions using supported, nanoscale zero-valent iron. Environ. Sci. Technol. 34 (12), 2564e2569. Qian, Q., Mochidzuki, K., Fujii, T., Sakoda, A., 2009. Removal of copper from aqueous solution using iron-containing adsorbents derived from methane fermentation sludge. J. Hazard. Mater. 172 (2e3), 1137e1144. Reynolds, T.M., Richards, P.S., 1996. Unit Operations and Processes in Environmental Engineering. PSW Publishing Co., Boston, p. 364. Schwertman, U., Taylor, R.M., 1989. Iron oxides. In: Dixon, J.B., Weed, S.B. (Eds.), Minerals in Soil Environments, second ed., pp. 379e428 Soil Sci. Soc. Am. J., Medison, Wisconsin, USA. Scott, T.B., Popescu, I.C., Crane, R.A., Noubactep, C., 2011. Nanoscale metallic iron for the treatment of solutions containing multiple inorganic contaminants. J. Hazard. Mater. 186 (1), 280e287. Shama, S.A., Moustafa, M.E., Gad, M.A., 2010. Removal of heavy metals Fe3þ, Cu2þ, Zn2þ, Pb2þ, Cr3þ and Cd2þ from aqueous solutions by using eichhornia crassipes. Portugaliae Electrochim. Acta 28 (2), 125e133.
Shi, L.N., Zhang, X., Chen, Z.L., 2011. Removal of chromium (VI) from wastewater using bentonite-supported nanoscale zerovalent iron. Water Res. 45 (2), 886e892. Shokes, T.E., Moller, G., 1999. Removal of dissolved heavy metals from acid rock drainage using iron metal. Environ. Sci. Technol. 33 (2), 282e287. Thiruvenkatachari, R., Vigneswaran, S., Naidu, R., 2008. Permeable reactive barrier for groundwater remediation. J. Ind. Eng. Chem. 14 (2), 145e156. Uzum, C., Shahwan, T., Erolu, A.E., Hallam, K.R., Scott, T.B., Lieberwirth, I., 2009. Synthesis and characterization of kaolinite-supported zero-valent iron nanoparticles and their application for the removal of aqueous Cu2þ and Co2þ ions. Appl. Clay Sci. 43 (2), 172e181. Vijayaraghavan, K., Jegan, J., Palanivelu, K., Velan, M., 2005. Batch and column removal of copper from aqueous solution using a brown marine alga Turbinaria ornate. Chem. Eng. J. 106 (2), 177e184. Wang, J., Qian, Y., 1999. Microbial degradation of 4-chlorophenol by microorganisms entrapped in carrageenan-chitosan gels. Chemosphere 38 (13), 3109e3117. Wan-Ngah, W.S., Fatinathan, S., 2008. Adsorption of Cu (II) ions in aqueous solution using chitosan beads, chitosan-GLA beads and chitosan-alginate beads. Chem. Eng. J. 143 (1e3), 62e72. Wan-Ngah, W.S., Hanafiah, M.A.K.M., Yong, S.S., 2008. Adsorption of humic acid from aqueous solutions on crosslinked chitosan-epichlorohydrin beads: kinetics and isotherm studies. Colloid Surf. B 65 (1), 18e24. Wilkin, R.T., McNeil, M.S., 2003. Laboratory evaluation of zerovalent iron to treat water impacted by acid mine drainage. Chemosphere 53 (7), 715e725. Xiu, Z.M., Jin, Z.H., Li, T.L., Mahendra, S., Lowry, G.V., Alvarez, P.J.J., 2010. Effects of nanoscale zero-valent iron particles on a mixed culture dechlorinating trichloroethylene. Bioresour. Technol. 101 (4), 1141e1146. Zhan, J., Sunkara, B., Le, L., John, V.T., He, J., McPherson, G.L., Piringer, G., Lu, Y., 2009. Multifunctional colloidal particles for in situ remediation of chlorinated hydrocarbons. Environ. Sci. Technol. 43 (22), 8616e8621. Zhang, H., Alsarra, I.A., Neau, S.H., 2002. An in vitro evaluation of a chitosan-containing multiparticulate system for macromolecule delivery to the colon. Int. J. Pharm. 239, 197e205. Zhang, M., He, F., Zhao, D., Hao, X., 2011. Degradation of soilsorbed trichloroethylene by stabilized zero valent iron nanoparticles: effects of sorption, surfactants, and natural organic matter. Water Res. 45 (7), 2401e2414.
Please cite this article in press as: Liu, T., et al., Enhanced chitosan beads-supported Fe0-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers, Water Research (2013), http://dx.doi.org/10.1016/ j.watres.2013.09.006